The businessman-servant duo from Noida, accused of serial killings of minor children of Nithari village, on Sunday underwent polygraph and brain mapping at the Directorate of Forensic Sciences, officials said in Gandhinagar.

Moninder Singh Pandher and his servant Surendra Koli were subjected to the tests, which were likely to continue till late night, DFS Director J M Vyas told reporters.

Narco analysis tests will be conducted on them on Monday, Vyas said.

Both accused have been cooperating for the tests, he added. This is the third day of forensic tests on the two.

The CBI team is likely to reach the city on Sunday to take them into custody as the Uttar Pradesh government has transferred the case to it, police sources said.

DFS officials are tight-lipped about their investigation.

They were also subjected to detailed medical examination on Saturday at Gandhinagar Civil Hospital.

DFS sources said the medical tests were a prelude to the narco-analysis or "truth serum" tests on the accused and it was during the test that it was revealed that Surendra was diabetic.

Police sources also said on the first day of the crucial forensic tests that prime accused Moninder had revealed his high-profile connections with ministers and others who frequented his Noida residence.

DFS officials will also improve the line of questioning, type of audio and video probes that will be provided to the two to get them to respond truthfully to details of the case.